The present invention relates to a fixing device, for example, for use in fluid control apparatus which are assembled by fixing a plurality of couplings to a base plate and fixing on-off valves each to some of the couplings, the device being useful for fixing the couplings (lower members), to be disposed between the base plate (support member) and the on-off device (upper member), to the base plate (support plate).
The terms xe2x80x9cupperxe2x80x9d and xe2x80x9clowerxe2x80x9d as used herein refer respectively to the upper and lower sides of the drawings. However, these terms are used for the sake of convenience; the fixing device and the fluid control apparatus will be mounted on a horizontal surface, for example, in the illustrated state or as turned upside down, or may be attached to a vertical surface.
For example in fluid control apparatus for use in manufacturing semiconductors, etc., the lower members, i.e., coupling members having bolt bores, to be disposed between a support member and an upper member, i.e., an on-off valve, are fixed to the support member with bolts. To provide a fluid-tight joint between each lower member and the upper member in this case, a seal portion is formed between these members.
The conventional fluid control apparatus has the problem that when the lower members are fixed to the support member, the upper surfaces of the lower members are not always flush with each other, presenting difficulty in mounting the upper member on the lower members. If the upper member is mounted on the lower members with the upper surfaces of the lower members positioned at different levels, there arises the problem that different pressures acting on the seal portions produce a faulty seal.
To obviate this problem, we have proposed a fixing device for lower members as shown in FIG. 5 (see Japanese Patent Application 258075/1997).
The proposed device is adapted to fix lower members 31, 33 to a support member 108 with bolts 110, the lower members each having a bolt bore 107 and being disposed between the support member 108 and an upper member 7, the fixing device being characterized in that the bolt bore 107 of each of the lower members 31, 33 comprises a large-diameter portion 107a larger than the head 110a of the bolt in diameter, and a small diameter portion 107b extending downward from the large-diameter portion with a stepped portion 107c formed therebetween and having a diameter intermediate between the diameter of the bolt head 110a and the diameter of the shank 110b of the bolt, the small-diameter portion 107b of the bolt bore having fitted therein a hollow cylindrical spacer 111 with an inside diameter larger than the diameter of the bolt shank 110b,the spacer 111 having a lower end supported by the support member 108 and an upper end positioned in the large-diameter portion 107a, a hollow cylindrical elastic member 112 being interposed between the bolt head 110a and the stepped portion 107c for biasing the lower member toward the support member 108.
With fluid control apparatus having such lower member fixing devices, it is likely that a heater will be installed for preventing condensation of water vapor and for preventing re-liquefaction to be involved in passing a fluid, which is liquid at room temperature, as converted to a gas. In this case, a heat insulating material of Teflon (polytetrafluoroethylene=PTFE) or the like is interposed between the lower member which is made of stainless steel or like metal and the support member which is made of metal such as aluminum or stainless steel.
An object of the present invention is to provide a device for fixing lower members to a support member which device is suitable for use in interposing a heat insulating material between the support member and the lower members, and a fluid control apparatus having the fixing device incorporated therein.
The present invention provides a device for fixing lower members to a support member by bolts (110) with a heat insulator interposed between the support member and the lower members, the lower members each having a bolt bore and being disposed between the support member and an upper member, the fixing device being characterized in that the bolt bore of each of the lower members comprises a large-diameter portion larger than a head of the bolt in diameter, and a small diameter portion extending downward from the large-diameter portion with a stepped portion formed therebetween and having a diameter intermediate between the diameter of the bolt head and the diameter of a shank of the bolt, the heat insulator being formed with a spacer inserting hole, a hollow cylindrical spacer having an inside diameter larger than the diameter of the bolt shank and being inserted through the small-diameter portion of the bolt bore and the spacer inserting hole so that an upper end of the spacer is positioned in the large-diameter portion, the spacer having a lower end bearing on the support member, a hollow cylindrical elastic member being interposed between the bolt head and the stepped portion for biasing the lower member toward the support member.
The elastic member, which is preferably a rubber washer, may alternatively be a compression coil spring equivalent to the rubber washer in modulus of elasticity.
As each bolt of the lower member fixing device is tightened, the spacer is held between the bolt head and the support member, preventing further tightening. The elastic member biases the lower member toward the support member at this time, obviating the backlash of the lower member. On the other hand, the compression of the elastic member moves the lower member, having its upper surface positioned at a lower level than the other lower member, in a direction away from the support member, whereby the upper surfaces of the lower members can be made flush with each other. This renders the upper member easy to mount on the lower members. The heat insulator is more dependent on temperature and alters more markedly in properties with the lapse of time than the support member and the lower member which are both made of metal. It is accordingly likely that a clearance will be created between the heat insulator and the support member or the lower member, whereas even in such a case, the fixing device maintains a predetermined interval between the support member and the lower member, pressing the lower member against the support member with a suitable force to eliminate backlashes.
The lower member fixing device is suitable for use in fluid control apparatus which require a heater. For example, the lower members serve as couplings each having an upwardly open fluid channel, and the upper member as an on-off valve having two fluid channels which are open downward and communicate with the fluid channels of the lower members respectively, for use in the fluid control apparatus. A fluid channel is then formed which extends from one of the couplings to the other coupling by way of the on-off valve. The desired fluid control apparatus can be fabricated using such couplings, on-off valves and other fluid controllers in combination. Useful as the heater is, for example, a tape heater which is provided along, and in contact with, one or each of opposite side surfaces of at least one of the lower members, but the heater is not limited only to this type of heater.
In such fluid control apparatus, it is desirable to provide a seal between butting faces of each lower member and the upper member around the junction of the opposed fluid channels of these members. The lower members can then be joined to the upper member as made fluidtight by the seals, while the upper surfaces of the lower members can be rendered flush with each other, thereby permitting a uniform force to act on the seal portions.